Update 8/2011 - modifications to make this beret in 2 colors posted here.
Just uploaded the pattern for the Quick Slouchy Brioche Beret over on Ravelry. This was test knit three times, with iterations to the top each time. The last iteration has a smoother top that I prefer.
Any super bulky yarn should work for this hat. The band measures 19" but will easily stretch to 21-22".
The link to the pattern can be found over on the right hand side under the complementary patterns section. I've used the terms and abbreviations standardized by Nancy Marchant in her book, Knitting Brioche, 2010. More information on brioche stitch is available at Nancy's website: www.briochestitch.com/
As always, please contact me with any questions, comments or concerns. If you knit up this pattern, please consider posting a project with pics over on ravelry so we can all share!